Method and apparatus for stopping and starting one or more open-end-spinning devices

ABSTRACT

Yarn breakages or irregularities are avoided by connecting spinning apparatus, fiber sliver supply devices, and yarn drawoff devices by suitable mechanical connections to a common variable speed motor to maintain a constant speed ratio between such components of spinning apparatus. A plurality of spinning apparatuses may have individual drive motors connected electrically to the common motor. Interposed between the main operating switch and the drive motor are a pair of intermediate circuits, one circuit having a potentiometer control to limit the motor to a low variable speed range, and the second circuit having relatively high speed range including normal production speed. Selector switches cooperate to connect the drive motor to one or the other of the intermediate circuits, but one or more of such selector switches may be operable manually or by cam control drums to effect switching from one intermediate circuit to another to effect low speed operation for an indefinite or a predetermined time to facilitate bobbin-changing or return of an escaped yarn end, for example.

United States Patent Landwehrkamp et al.

METHOD AND APPARATUS FOR STOPPING AND STARTING ONE OR MORE OPEN-END-SPINNING DEVICES Inventors: Hans Landwehrkamp, Gerolfing;

Heinrich Niestroj, Ingolstadt, both of Germany Schubert & Salzer Maschinenfabrik Aktiengesellschaft, Ingolstadt, Germany Filed: Nov. 18, 1971 Appl. No.: 200,024

Assignee:

Foreign Application Priority Data Nov. 28, 1970 Germany 2058604 June 21, 1971 Germany 2130669 [56] References Cited UNITED STATES PATENTS 1,719,889 7/1929 Kelsey 318/228 X 2,275,570 3/1942 Snyder 57/100 2,946,178 7/1960 l-lamel 57/100 3,316,699 5/1967 Mattingly 57/100 X 11/1967 Cizek et al 57/58.89 X 11/1970 Sterba et al 57/58.95 X

Primary ExaminerJohn Petrakes Assistant ExaminerCharles Gorenstein Attorney, Agentfor Firm Robert W. Beach; R. M. Van Winkle ABSTRACT Yarn breakages or irregularities are avoided by connecting spinning apparatus, fiber sliver supply devices, and yarn drawoff devices by suitable mechanical connections to a common variable speed motor to maintain a constant speed ratio between such components of spinning apparatus. A plurality of spinning apparatuses may have individual drive motors connected electrically to the common motor. Interposed between the main operating switch and the drive motor are a pair of intermediate circuits, one circuit having a potentiometer control to limit the motor to a low variable speed range, and the second circuit having relatively high speed range including normal production speed. Selector switches cooperate to connect the drive motor to one or the other of the intermediate circuits, but one or more of such selector switches may be operable manually or by cam control drums to effect switching from one intermediate circuit to another to effect low speed operation for an indefinite or a predetermined time to facilitate bobbin-changing or return of an escaped yarn end, for example.

8 Claims, 4 Drawing Figures PATENTEDFEB 12 I974 sum 2 or 2 METHOD AND APPARATUS FOR STOPPING AND STARTING ONE OR MORE OPEN-END-SPINNING DEVICES BACKGROUND OF INVENTION 1. Field to which Invention Relates The present invention relates more particularly to a method and apparatus for stopping and starting one or more open-end-spinning devices.

2. The Prior Art In the case of open-end-spinning devices the fibre material supplied is in the form of a sliver and is introduced in an opened condition into a spinning element, from which it is removed as a thread in the ready spun condition. On stopping the open-end-spinning device, the latter is separated from its drive by a coupling or a clutch and for the starting operation the open-endspinning device is connected by a coupling with its drive (see Swiss specification No. 443,081 and East German specification No. 63,308). The spinning device thus always operates with a constant speed of production, the speed of rotation of the spinning element, the feed speed and the drawoff speed for the yarn or thread being selected in accordance with the material, desired yarn number and twist by changing the transmission ratio. Stopping and starting spinning are thus carried out with the desired production speed.

Purely from the spinning point of view high production speed could be achieved, but substantial difficulties occur on stopping and starting spinning which lead more particularly to yarn breakages and lack of yarn regularity. In particular it has been found that starting spinning must occur within a definite period of time, which depends on the production speed. If this period of time for starting spinning is departed from by making the period too long or too short, starting operations lead to yarn breakages or thickened parts in the yarn which has been pieced up. Thus, starting spinning requires a high degree of skill from the machine operator. In the case of spinning turbines the danger of yarn breakage is made still greater by the fact that if drawoff is started too late the yarn end provided for piecing up is excessively twisted or does not stand up to the high centrifugal force occurring with the high speed of rotation of the turbine. In order to ensure that, upon stopping a spinning device with a spinning turbine, the yarn end comes out of its position adjacent to the fibre collecting groove, but nevertheless remains within the yarn drawoff tube, it is necessary to keep to a different stopping time in accordance with the speed of working. For this purpose complicated devices are necessary which must also be adjustable to suit the speed of working to be tried out.

SUMMARY OF INVENTION One aim of the invention is therefore to provide a method for stopping and starting one or more openend-spinning devices and also a simple and secure device for carrying out the method, with whose help the danger of faults such as yarn breakages or thick or thin parts is avoided or at least substantially reduced.

The present invention consists in a method for stopping and starting at least one open-end-spinning device, characterised in that the stopping and starting are carried out while maintaining the speed ratios between the driven elements, such as fibre supply, yarn drawoff, and the spinning element at a low yarn drawoff speed at which various servicing operations can be carried out. As a result for stopping the spinning device and for starting it again comparatively long periods of time are available, timing tolerances are correspondingly larger and the danger of faults occurring is substantially reduced. However, the method of the present invention not only facilitates starting-up spinning after stopping the spinning device or a whole spinning machine, but also simplifies restarting spinning after dealing with a yarn breakage. In accordance with the invention a manually effected change in bobbins is carried out while maintaining the speed relationship between the driven elements of the spinning device at a low yarn drawoff speed. Since the speed ratios remain unchanged, these changes in speed can be carried out without the yarn quality or characteristics being changed. Conveniently the low drawoff speed can always have the same value, independently of the actual production speed used.

For carrying out such a method it would be obvious to ensure that the speed is changed in steps by the use of a mechanical or electrical variable speed drive. Such a construction is, however, extraodinarily complicated.

Therefore, the invention further consists in an apparatus for stopping an open-end-spinning device, comprising means defining a spinning chamber, a fibre supply device, a yarn drawoff device, a main switch, a drive motor which serves for driving the fibre supply device and the fibre drawoff device and which can be switched off and on by means of the main switch, at least two potentiometers connected in parallel between the main switch and the drive motor, and at least one change-over switch between the potentiometers and the drive motor. The change-over switch makes possible the selective switching-over from one potentiometer to the other and in this manner determines the speed of rotation of the drive motor. In order to be able to control the switching-over operation both automatically, and also manually when desired, preferably several switching-over switches are provided in tandem so that one can override the other, at least one switchingover switch being provided with a timing member which, after the expiry of a certain period of time following actuation of such member, actuates the for switching from the potentiometer for slow running speed to the potentiometer for highspeed running of the drive motor. The timing member can be constructed in various different manners, for example as a timing relay. Preferably the timing member, however, consists of a control drum. Since the switching-over operation is subject to larger variations in timing than the starting operation for the open-end-spinning machine, it is preferable that not only starting but also the stopping of the spinning machine should be arranged to be carried out with the help of the control drum so that both switching-over operations can be carried out automatically. In accordance with a particularly simple and advantageous construction, the control drum for stopping can be coupled with the drive motor in such a manner that the control drum is driven synchronously with the drive motor.

LIST OF SEVERAL VIEWS OF DRAWINGS The invention will now be described with reference to the accompanying drawings.

FIG. '1 is a diagrammatic view of the subject matter of the invention.

FIG. 2 shows diagrammatically a different embodiment of the subject matter of the invention with a timing member for starting spinning.

FIG. 3 shows a further construction diagrammatically with separate control drums for starting spinning and stopping spinning.

FIG. 4 shows part of a further embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS For the constructions embodying the invention it is important that stopping and starting spinning of one or more open-end-spinning devices must be carried out within a period of time depending on the actual speed of production. The higher the speed of production of the opemend-spinning machine, the higher are the requirements which are set as regards operating machine. The consequence is piecing-up faults such as thick or thin parts of the yarn or yarn breakages increase exponentially with the production speed.

It is quite possible for open-end-spinning machines to operate with a drawoff speed of, for example, 150 metres per minute and more. With such a drawoff speed, starting spinning by hand is hardly possible or can only be carried out with great difficulty. Furthermore, at these speeds a change in bobbin can hardly be carried out.

In the constructions in accordance with the invention, therefore, the operations for starting spinning and the changing of bobbins are carried out at a lower drawoff speed of the spinning device. In this respect it is only necessary to ensure that the ratio between the speed of rotation of the spinning element (if the spinning element should not be stationary), of the fibre supply and the yarn drawoff speed is kept constant. Owing to this feature it is possible to control the speed with the help of a simple device, and the machine operator has sufficient time for starting spinning the thread or the changing of bobbins.

FIG. 1 shows a first embodiment of the subject matter of the invention, parts not absolutely necessary for understanding the invention being omitted.

The spinning element is mounted in a conventional manner in a housing 1 and is driven by a belt 10, while the belt is driven by a drive motor 2 via a shaft and a belt pulley 21. Furthermore, on the shaft 20 a bevel gear wheel 23 is mounted, which via a bevel gear wheel 24 drives a shaft 25 with the drawoff rollers 26. The drawoff rollers 26 can be sepated from the drive in a conventional manner with the help of a coupling 27. The shaft 25 drives via a chain 28 or other suitable transmission the winding-up device, not shown, for the yarn 29 and via a chain 11 it drives an opening roller, arranged on the shaft 12, of the supply device 13. From the shaft 12 the supply roller of the supply device 13, is driven via a chain 14, a shaft 15 and a belt 16.

The drive motor 2 can be connected through main switch 3 with the three phase main line. For controlling this drive motor two potentiometers 4 and 40 are provided which can be connected by the main switch 3 with a DC current source for the control circuit. The potentiometers 4 and 40 are connected with a changeover switch 41 arranged between them and the drive motor 2. Between this change-over switch 41 and the drive motor 2 there is furthermore a starting device 42 for starting up the motor and an amplifier 43.

In order to be able to see at which speed the motor 2 is running at any particular instant, a tachometer 22 is connected with the shaft 20.

The arrangement whose construction has just been described operates in the following manner.

Firstly the open-end-spinning machine is switched on to start the machine from zero speed, which constitutes the lower limit speed by actuating the main switch 3 and the change-over switch 41 is connected with the potentiometer 4. This potentiometer serves for selecting the low speed for starting spinning and changing bobbins. Thus, the drive motor 2 can be accelerated in the manner determined by the starting device 42 only as far as the speed determined by the potentiometer 4, and simultaneously the spinning element 1, the drawoff rollers 26 and the supply device 13 only reach the low speed determined by the transmission ratio. In this manner the drawoff rollers 26 can be switched on with a time lag, so that the quantity of fibre necessary for starting spinning can be supplied to the spinning element. For this purpose the coupling 27 is provided, which is controlled in a suitable manner, for example by a timing relay actuated by the main switch 3.

When the speed determined by the potentiometer 4 has been reached, as can be seen by reading the tachometer 22, starting spinning at all spinning positions can be carried out in a conventional manner by supplying the yarn back into the spinning devices.

When spinning has been restarted, the potentiometer 40 is connected through the change-over switch 41 with the starting device 42 so that the drive motor 2 is brought up to the full production speed which constitutes the upper limit speed.

On stopping spinning a certain time is to be kept to in accordance with the speed of production. If drawing off is stopped too early, the yarn end is excessively twisted in the spinning element and forms a knot which on piecing up produces a thickened portion in the yarn or alternatively immediately leads to yarn breakage. If, on the other hand, drawoff is stopped too late, the yarn end is drawn out of the drawoff tube so that the following spinning operation must be carried out by hand. In the case of a spinning turbine, for example with a radius of 25 mm and a periphery of mm, the piece of yarn located in the spinning turbine has a length of mm. If the drawoff speed is 60 metres per minute, that is to say 1 mm per millisecond, drawoff must be switched off within 185 milliseconds. In the same condition the stopping of draw-off at a draw-off speed of 100 meters per minute must be effectuated within 1 l 1 milliseconds while in the case of a drawoff speed of 30 metres per minute 370 milliseconds are available.

For reducing the draw-off speed to zero, that is, to a rest speed for stopping the open-end-spinning machine the changeover switch 41 is moved over to provide a connection with the potentiometer 4. The drive motor 2 is slowed down until the low speed, intermediate of the rest speed and full production speed, determined by the potentiometer 4 is reached. At the slower speed after the stopping of the supply device 13, the correctly timed declutching of the coupling 27 for the drawoff roller 26 can be carried out without difficulty using time relays and the like so that one can be sure that the yarn 29 is not drawn out owing to excessively late stopping of the drawoff rollers 26 from the spinning element.

Since the speed ratios between the individual driven elements of the spinning machine remain constant, the production speed can be reduced by hand, in the case of individual restarting of spinning or for bobbin changing, so that the drawoff speed necessary for this purpose is achieved without yarn quality sufiering as a result. For this purpose the drive motor 2 is slowed by manual actuation of the change-over switch 41 down to the low speed determined by the potentiometer 4 so that for this working operation a comparatively long period of time is available. After conclusion of the bobbin changing operation or of individual restarting of spinning the potentiometer 40 is again connected with the change-over switch 41 so that the drive motor 2 is accelerated up to the full production speed again.

FIG. 2 shows a different embodiment of the subject matter of the invention in which two change-over switches 44 and 45 are arranged in tandem so as to provide an overriding function, the subordinate changeover switch 44 being provided with a control disc 5 to act as a timing member. The control disc 5 is driven by an auxiliary motor 50 which can be switched on by the main switch 30. A further control disc 51, also driven by auxiliary motor 50, opens a contact 52 when the switching on operation is concluded, that is when switching-over of the change-over switch 44 to the potentiometer 40 has been effected, to deenergize motor 50.

At the time of starting the spinning machine by actuating the main switch 30, the two change-over switches 44 and 45 are in the position shown. Thus, the starting device 42 for the drive motor 2 is connected with the potentiometer 4 so that the drive motor 2 can initially only be accelerated up to the maximum speed determined by setting this potentiometer 4. By operation of the main switch 30 and the simultaneous actuation of the switch 32 for a short period of time, the switch 32 overriding the contact 52, the auxiliary motor 50 is also connected with the current supply and starts the control discs 50 and 51. After a certain degree of rotation a cam element 53 on the control disc 5 releases the change-over switch 44, which now connects the highspeed potentiometer meter 40 with the starting device 42 so that the drive motor 2 now runs up to full speed. On further rotation of the control discs 5 and 51 the contact 52 is opened by a cam element 54 on the control discSl. Since the switch 32 is only closed during the time at which switching-on takes place, the current circuit for the auxiliary motor 50 is now interrupted and the latter remains inactive.

If for individual restarting by hand, for bobbin changing or for starting the stopping operation the speed is to be reduced to the low speed determined by the potentiometer 4, the change-over switch 45 is operated by hand. On releasing the change-over switch the spinning machine is accelerated again up to the full production speed. If, however, the main switch 30 is opened before switch 45 is released, the spinning machine is stopped.

It is not absolutely essential for the timing member for the actuation of the change-over switch 44 to be constructed as a control disc 5 and it is possible instead to use a timing relay. Since, however, not only the change-over switch 44 but also the fan of the vacuum shaft (if provided), the couplings (not shown) for the individual supply devices 13, the coupling 27 for the draw-off rollers, the yarn monitoring device (not shown), and other parts must be put into operation at precisely determined instants in time, a control disc or control drum (FIG. 3) constituting a timing member is particularly advantageous.

The embodiment of the subject matter of the invention shown in FIG. 3 comprises three change-over switches 44, 45 and 46 with an overriding function, the change-over switch nearest to the starting device 42 being arranged to override the change-over switches arranged further from the starting device. The changeover switch 46 is thus arranged to override the changeover switches 45 and 44, while the change-over switch 45 overrides the change-over switch 44 as is the case with the embodiment shown in FIG. 2.

The change-over switch 44 is again actuated by a cam element 53 which in this case is arranged on a control drum 55 driven by the auxiliary motor 50. The change-over switch 45 serves for hand actuation while the change-over switch 46 is controlled by a relay 47.

In the case of this device a switching-on switch 31 is provided with the parallel connected switch or contact 32 for the auxiliary motor 50 for opening the contact 52 for a short period of time. The on-switch 31 actuates the relay or a contactor 33, which has a control contact 33a for the potentiometers 4 and 40, a self-holding contact 33b, three contacts 330 for the current supply to the drive motor 2 and a contact 33d for the auxiliary motor 50. Furthermore, an off-switch 34 is provided which actuates a relay or contactor 35. This relay or contactor has a control contact 35a for the abovementioned relay 47 and a self-holding contact 35b.

As already mentioned on stopping the machine, such machine is first reduced to a low speed and then switched off completely. In order for it to be possible to use a constant timing member for the switching-off operation, for example a switching roller, the switching-off is not carried out in accordance with the invention at an arbitarily chosen lower speed but at a low drawoff speed which is always the same and is independent from the normal drawoff speed. It is thus possible to use simple means to ensure that only the same length of yarn is drawn from the point of engagement of the spinning element. In this respect it is of no importance for the invention Whether the drawoff of this length of yarn is carried out by delayed switching-off of the drawoff rollers or by providing a particular drawoff member, for example a deviator bar, for forming a yarn reserve for later yarn piecing-up.

For this circuit the drawoff speed is kept as low as possible in order that the time available is large and the small errors in time of the switching parts do not have such large percentage effects.

In the case of the construction shown in FIG. 3, for this reason a control drum is provided not only for the starting of spinning but another control drum is provided for stopping the spinning machine. This control drum 6 has, inter alia, cam elements and 61, of which the cam element 60 controls a contact 36, arranged in the holding circuit of the relay or the contactor 33, and the cam element 61 controls a contact 37 in the holding circuit of the relay or contactor 35. The control drum 6 can be connected with drive motor 2 by means of a coupling 62 controlled by the relay 47.

On actuation of the switch 31 the relay or the contactor 33 is excited, which closes its contacts 330 to 33d. As a result the two potentiometers 4 and 40 and the drive motor 2 are connected with the current supply. Upon actuation of the on-switch 31 the contact 32 is closed for a short period of time to override the normally-open contact 52 until the cam element 54, driven by the auxiliary motor 50, closes the contact 52. Consequently, contacts 32 and 52 are connected in parallel so that closing of either contact will actuate motor 50. The change-over switch 44 is connected with the potentiometer 4 by the cam elemet 53 so that the drive motor 2 can initially only be accelerated up to the low speed. After this speed has been achieved, the cam element 53, whose length is chosen accordingly, releases the change-over switch 44 so that the latter is connected with the potentiometer 40 and the drive motor 2 and the devices driven by the latter now reach the full production speed. Shortly after this the cam element 54 releases the contact 52 to interrupt the supply of current to the auxiliary motor 50 and the control drum 55 remains stationary.

If for any reason, for example for individual manual restarting of spinning or for changing bobbins, the speed of the machine must be lowered, the change-over switch 45 is suitably operated by hand.

The stopping of the spinning machine is carried out as follows:

By actuation of the off-switch 34 the relay or the contactor 35 is excited, which closes its contacts 35a and 35b and as a result the relay 47 is also excited which connects the change-over switch 46 with the potentiometer 4 for the low speed and through its contact 48 supplies the coupling 62 with current. The coupling 62 connects the control drum 6 with the drive motor 2 so that the drum is driven, in accordance with the speed of rotation of the drive motor 2 via the step-down gearing 63, at a correspondingly lower speed of rotation. Thus, all operations controlled by the control drum 6, such as switching-off of the yarn monitor, fibre supply and drawoff are carried out synchronously with the reduction of speed of the drive motor 2. After a certain time has expired, the holding circuit of the relay or contactor 33 is interrupted by the opening of the contact 36 by cam 60 and the relay or contactor 33 is opened so that the potentiometer 4 is no longer supplied with current and the drive motor 2 is stopped. Before it stops, the drive motor 2 turns the control drum somewhat further until the cam element 61 opens the contact 37 in the holding circuit of the relay or contactor 35. And as a result the relay or contactor 35 and the relay 47 dependent on it are de-energised and consequently the coupling 62 cuts off the control drum 6 of the drive motor 2 so that the control drum stops.

The subject matter of the invention is subject to numerous possible modifications. Thus, the relay 47 can be a timing relay which actuates the coupling 62 only after a certain time has expired. The relay can also, however, be actuated by the tachometer 22 (FIG. 2) when the drive motor 2 has been slowed down to a certain low speed which has been previously determined. In this respect the reduction in speed can be aided by a brake controlled by the off-switch 34.

The spinning element can be driven by an individual drive motor 17 (FIG. 2) in accordance with the speed of rotation of the drive motor 2 instead of via a belt 10, the drive motor 17 being connected electrically with the tachometer 22.

Preferably the control drum 6 can be connected by a coupling 62 with the drive motor 2, though it is possible, instead of this connection, to provide an individual auxiliary motor similar to that in the case of the control drum 55. Or, on the other hand, the control drum 55 may be arranged to be capable of being coupled with the drive motor 2.

It is also possible to provide more than two potentiometers if this should be considered to be convenient and with their help various different production speeds can be capable of being set. In accordance with FIG. 4, for example, three potentiometers 4, 40 and 49 are provided. The potentiometer 4 is provided for controlling the lowest speed and the potentiometer 49 is provided for controlling the highest speed. These three potentiometers are provided, in the example shown, with two change-over switches 7 and 70. Each change-over switch can assume three positions, in accordance with the number of potentiometers. The change-over switch 7 is actuated by an off-set cam element and the changeover switch is actuated by hand.

Instead of individual potentiometers 4, 40 and 49 it is also possible to provide groups of potentiometers. In this case, for example, two potentiometers per potentiometer group serve for determining the upper and lower limit of a speed range while the third potentiometer is used for the actual setting of the speed within the respective range.

The construction of the spinning elements is of no consequence for the present invention. The spinning elements can, for example, be used in conjunction with spinning turbines (U. S. specification No. 3,440,812), rotating or stationary spinning funnels (Czech specification No. 87,947, French specification No. 1,442,699, or chambers in which the fibres moving with a medium become attached to a freely rotating yarn end (U.S. specification No. 2,91 1,783).

The invention makes possible a simple automatic and also manual operation for the critical phases of starting spinning after stopping the machine, or on dealing with a yarn breakage which cannot be dealt with automatically, or bobbin changing can be carried out at a lower working speed. Since the speed ratio between the individual devices of the open-end-spinning machine always remains constant, the changes in speed are also not apparent in the finished yarn.

We claim:

1. A method for stopping an open-end-spinning device including spinning chamber means, sliver feed means and yarn drawoff means, all of said means being driven at constant speed ratios in relation to each other, comprising the steps of decelerating the spinning device from the full spinning speed to a selected low speed while maintaining said constant ratio, stopping the spinning device only after such selected low spinning speed has been reached, and subsequently starting the open-end-spinning device by accelerating the spinning speed up to a selected low speed, feeding a yarn end back into the spinning device and only thereafter accelerating the spinning speed up to full spinning speed.

2. A method of exchanging yarn-receiving bobbins in an open-end-spinning device including yarn-receiving bobbins, spinning chamber means, sliver feed means and yarn drawoff means, all of said means being driven at constant speed ratios in relation to each other, comprising the steps of reducing the spinning speed to a selected low speed while maintaining said constant ratio, manually exchanging a yarn-receiving bobbin, and again accelerating the spinning speed up to full speed after the yarn-receiving bobbin has been exchanged.

3. A method of repairing yarn breakages in an openend-spinning device including spinning chamber means, sliver feed means and yarn drawoff means, all of said means being driven at constant speed ratios in relation to each other, comprising the steps of reducing the spinning speed to a selected low speed while maintaining said constant ratio, repairing a yarn breakage, and again accelerating the spinning speed to full speed after said repairing operation has been effected.

4. A method for effecting servicing operations in an open-end-spinning device having two limit speeds, one being rest speed and the other being full speed, said open-end-spinning device including chamber means, sliver feed means and yarn drawoff means, all of said means being driven at constant speed ratios in relation to each other even during changing from one limit speed to the other, comprising the steps of changing from one limit speed to an intermediate, relatively low, speed, holding such intermediate speed constant, effecting a servicing operation, and subsequently changing from said intermediate speed to one of the limit speeds.

5. Speed control apparatus for an open-end-spinning device having spinning means, a fiber supply device and a yarn drawoff device comprising drive means for driving the fiber supply device and the yarn drawoff device, main switch means for supplying power to said drive means, two potentiometer means connected in parallel between said drive means and said main switch means, and selector switch means operable to selectively connect drive means and one of said potentiometer means, said selector switch means including a plurality of selector switches, each operable between a position for forming a series connection between one potentiometer means and the drive means and a bypass position for connecting the drive means and the other potentiometer means, and timing means engageable with one of said selector switches to control its position and the length of time that such one selector switch is held in one of its positions.

6. The speed control apparatus defined in claim 5, in which the timing means includes a control drum.

7. The speed control apparatus defined in claim 6, further including auxiliary drive means, and coupling means for selectively coupling said auxiliary drive means and the control drum.

8. The speed control apparatus defined in claim 5, in which the timing means includes a first control drum to control increases in spinning speed, and a second control drum to control decreases in spinning speed. 

1. A method for stopping an open-end-spinning device including spinning chamber means, sliver feed means and yarn drawoff means, all of said means being driven at constant speed ratios in relation to each other, comprising the steps of decelerating the spinning device from the full spinning speed to a selected low speed while maintaining said constant ratio, stopping the spinning device only after such selected low spinning speed has been reached, and subsequently starting the open-end-spinning device by accelerating the spinning speed up to a selected low speed, feeding a yarn end back into the spinning device and only thereafter accelerating the spinning speed up to full spinning speed.
 2. A method of exchanging yarn-receiving bobbins in an open-end-spinning device including yarn-receiving bobbins, spinning chamber means, sliver feed means and yarn drawoff means, all of said means being driven at constant speed ratios in relation to each other, comprising the steps of reducing the spinning speed to a selected low speed while maintaining said constant ratio, manually exchanging a yarn-receiving bobbin, and again accelerating the spinning speed up to full speed after the yarn-receiving bobbin has been exchanged.
 3. A method of repairing yarn breakages in an open-end-spinning device including spinning chamber means, sliver feed means and yarn drawoff means, all of said means being driven at constant speed ratios in relation to each other, comprising the steps of reducing the spinning speed to a selected low speed while maintaining said constant ratio, repairing a yarn breakage, and again accelerating the spinning speed to full speed after said repairing operation has been effected.
 4. A method for effecting servicing operations in an open-end-spinning device having two limit speeds, one being rest speed and the other being full speed, said open-end-spinning device including chamber means, sliver feed means and yarn drawoff means, all of said means being driven at constant speed ratios in relation to each other even during changing from one limit speed to the other, comprising the steps of changing from one limit speed to an intermediate, relatively low, speed, holding such intermediate speed constant, effecting a servicing operation, and subsequently changing from said intermediate speed to one of the limit speeds.
 5. Speed control apparatus for an open-end-spinning device having spinning means, a fiber supply device and a yarn drawoff device comprising drive means for driving the fiber supply device and the yarn drawoff device, main switch means for supplying power to said drive means, two potentiometer means connected in parallel between said drive means and said main switch means, and selector switch means operable to selectively connect drive means and one of said potentiometer means, said selector switch means including a plurality of selector switches, each operable between a position for forming a series connection between one potentiometer means and the drive means and a bypass position for connecting the drive means and the other potentiometer means, and timing means engageable with one of said selector switches to control its position and the length of time that such one selector switch is held in one of its positions.
 6. The speed control apparatus defined in claim 5, in which the timing means includes a control drum.
 7. The speed control apparatus defined in claim 6, further including auxiliary drive means, and coupling means for selectively coupling said auxiliary drive means and the control drum.
 8. The speed control apparatus defined in claim 5, in which the timing means includes a first control drum to control increases in spinning speed, and a second control dRum to control decreases in spinning speed. 